To the editor:

The brief report by Kunishima et al1  describing a mutation of the β1 tubulin gene affecting microtubule assembly is of interest, but data presented do not support association of the genetic defect with macrothrombocytopenia. The authors stated both the male propositus and his mother had prominent appearance of giant platelets on peripheral blood smears, and provided light (Figure 1A1 ) and electron micrographs (Figure 1B1 ) to support that finding. The patient platelet in Figure 1A1  has damaged peripheral cytoplasm that may make it appear larger than a normal cell, but, more important, the platelet is significantly smaller than any red blood cell in the same field. No discoid platelets from the control or patient are present in the electron micrographs (Figure 1B1 ). As a result, it is difficult to be certain there is any real size difference between patient and control platelets. Surely the authors must be aware that giant platelets from all of the known macrothrombocytopenias are larger than red blood cells, and many exceed the size of lymphocytes, monocytes, and neutrophils.2  It might have been helpful if the authors had provided the mean platelet volumes of the mother and child.

The immunofluorescence studies raise 2 questions. Patient and control microtubule coils in the report's Figure 2A1  are similar in size and appear to be perfect coils. If the patients had complete platelet microtubule coils, those coils should be many times the diameter of control coils. More important, giant platelets from the known inherited macrothrombocytopenias rarely have complete microtubule coils lying just under the surface membrane. Rather, the giant platelets are spherical in form, and their microtubules are often organized in a manner resembling balls of yarn.3  The studies of the mutation in the present study are of interest. However, the statement “W318 β1 tubulin may interfere with normal platelet production, resulting in macrothrombocytopenia”1  is not supported by the data presented.

Conflict-of-interest disclosure: The author declares no competing financial interests.

Correspondence: James G. White, MD, Regents' Professor, Laboratory Medicine, Pathology, and Pediatrics, University of Minnesota School of Medicine, Mayo Bdg, Box MMC 490, 420 Delaware St SE, Minneapolis, MN 55455; e-mail: [email protected].

1
Kunishima
 
S
Kobayashi
 
R
Itoh
 
TJ
Hamaguchi
 
M
Saito
 
H
Mutation of the beta1-tubulin gene associated with congenital macrothrombocytopenia affecting microtubule assembly.
Blood
2009
, vol. 
113
 (pg. 
458
-
461
)
2
White
 
JG
Structural defects in inherited and giant platelet disorders.
Adv Hum Genet
1990
, vol. 
19
 (pg. 
133
-
234
)
3
White
 
JG
Sauk
 
JJ
The organization of microtubules and microtubule coils in giant platelet disorders.
Am J Pathol
1984
, vol. 
116
 (pg. 
514
-
522
)
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